使用data.table包重新编码变量 [英] Recode a variable using data.table package

问题描述

如果我想使用 data.table 在R中重新编码变量，语法是什么？我看到了一些ans，但没有找到合适的答案。

If I want to recode a variable in R using data.table, what is the syntax? I saw some ans but didn't find them appropriate.

例如如果我有一个名为 gender

e.g. if I have the variable called gender

的变量，我想将性别0重新编码为未知，1为男性，2为女：
这是我的尝试方式：

I want to recode gender 0 to unknown, 1 to male, 2 to female: here is how I tried:

Name <- c("John", "Tina", "Dave", "Casper")
Gender <- c(1, 2, 2, 0)

trips <- cbind.data.frame(Name, Gender)
trips[, gender = ifelse(gender == 0, "Unkown", gender == 1, "Male", gender == 2, "Female" )]

但我收到错误消息

推荐答案

一旦data.table，那么使用向量化翻译策略将是最有效的。 match 函数提供了一种创建选择向量的方法，用于从一组字符可能性中选择一项：

Once you have a data.table then it would be most efficient to use a vectorized translation strategy. The match function provides a method of creating a "selection vector" for a choosing a item from a set of character possibilities:

library(data.table)
setDT(trips)  # create a data.table from a dataframe

trips[ , Gender := c("Unknown", "male", "Female")[match(Gender, c(0,1,2))] ]
#-------------------
> trips
     Name  Gender
1:   John    male
2:   Tina  Female
3:   Dave  Female
4: Casper Unknown

对于这种特定情况，可以使用更简单的解决方案（将ht改为 @ Chinsoon ）：

For this specific case, a simpler solution could be (ht to @Chinsoon):

trips[, gender := c("Unknown", "Male", "Female")[gender + 1L] ]

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